The present invention relates generally to antennae systems, and more particularly to reflector antenna systems and feed structures for use therewith.
FIG. 1A illustrates a typical reflector antenna system 100 known in the art consisting of a reflecting dish 110 and an antenna feed structure 120. The reflecting dish 110 is typically of parabolic shape and has an inner concave surface constructed from a material which is highly reflective to the desired signal of operation. The feed 120 is placed at the focus of a parabolic dish for optimal performance in either collecting signal energy reflected from the dish 110, or transmitting signal energy to the dish's surface for subsequent transmission. In this particular configuration, the ratio of the reflector's focal distance to diameter f/D is greater than 0.25, a typical ratio being, for example, 0.5.
FIG. 1B illustrates the antenna pattern of the conventional feed 120 displaying E and H-plane signal responses. As shown, the edge of illumination at −10 dB is 106 degrees, representing the typical operational range from bore sight over which the antenna can transmit and receive signals.
FIG. 1C illustrates a high performance reflector antenna system 150 known in the art used to address the side lobe generation problem. In such a system, a shroud 160 is placed around the periphery of the reflector dish 110, and a radome 170 or other signal transparent material is used to enclose the feed structure 120 in the system. The shroud 160 includes a signal absorbing material on its inner surface for attenuating signals reflected from the feed structure 120. The result is reduced side lobe degradation, but at the cost of reduced antenna gain. Further, the improved antenna system 150 is even more limited in its field of view compared to the conventional system 100 because of the use of the shroud structure 160.
What is needed is a reflector antenna system which exhibits low side lobe performance without the use of absorbing material.